The invention relates generally to an electric shift control assembly for power transmission systems and more specifically to an electric shift control assembly for use in motor vehicle drive line components such as transfer cases and transmissions.
Shift assemblies, that is, devices which achieve selection of two or more gears or speed ranges in motor vehicle drive line components such as transmissions and transfer cases have evolved significantly over the years. Initially, such devices were exclusively manual, that is, actuated by the driver and comprised a plurality of parallel shift rails and forks which were selectively engaged and bi-directionally translated by an operator controlled shift lever.
With the advent of automatic transmissions, the shift lever became a mode selection device rather than a speed range selection device, the actual gear shifting occurring within the transmission, and generally without significant operator input.
Similarly, manual control of transfer case speed ranges has undergone an evolution from direct, manual control to selection by an electric, hydraulic or pneumatic operator controlled by direct driver input or a microprocessor. With direct, manual control, the shift mechanism may be similar to early transmission mechanisms including, for example, a single shift rail which may be moved bi-directionally to engage high gear, low gear and neutral. Numerous other mechanical arrangements are utilized to achieve high and low gear selection. For example, a shift fork may be slidably disposed on a fixed rail adjacent a rotatable shift rail. The rotatable shift rail is coupled to an energy storage device such as a spring which drives a cam engaged by a follower on the shift fork. The energy storage device stores energy so that shifts that cannot be immediately completed due to gear clash will be completed upon engageable alignment of gear teeth. Other assemblies utilizing, for example, rotating sector plates or ball screw actuators provide bi-directional motion to achieve such gear and speed selection.
When integrated with a microprocessor or other control system, it is commonly necessary to sense, in real time, the position of the shift member. Given such complex systems, it is generally advisable to detect such shift member position as proximate as possible to the actual components, i.e., the gears, achieving the shift. That is, if the assembly includes an energy storage device, it will be understood that the driving components of the mechanism may be in a position distinct from the driven components. Attempting to sense the position of the driven components from the drive components may thus readily introduce positional error. However, installing position sensors sufficiently proximate the driven or controlled element, i.e., the gears, may create significant packaging problems. Thus, gear shift operator assemblies wherein driving and driven components can be assured of always taking corresponding positions and thus permitting the position sensing to occur near the driving mechanism rather than the driven mechanism simplifies packaging and assembly issues. The present invention is directed to such an improved configuration.